Embryonic retina, superior colliculus or occipital cortex transplanted to the midbrain region of a newborn rat differentiates and forms extensive connections with appropriate visual nuclei in the host brain. These same fetal regions, when transplanted to the midbrain region of an adult rat, also survive and differentiate. However, in marked contrast to the newborn transplants, axonal outgrowth into the adult midbrain is very limited, extending a maximum of 6 mm into the host tissue. The project proposed here will further examine transplants of fetal retina, superior colliculus and cortex into adult brain in order to gain insight into ways in which this outgrowth can be increased as well as to further assess the potential use of these transplants as a clinical technique. The project has three major parts. First will be the examination in vitro of whether the presence of various glial populations, i.e. optic nerve glia, Muller cells, astrocytes, and Schwann cells, can facilitate neuritic outgrowth from explant cultures of embryonic and adult rat retina, tectum or cortex. Second will be to evaluate the possible ability of the various glial populations to increase axonal outgrowth from the transplants in vivo. This will involve the preparation of reaggregates of the embryonic visual system tissue combined with enriched populations of the various glial types. Third will be to determine if transplanted optic nerve or sciatic nerve grafts might be able to elicit and sustain outgrowth between areas of newborn or adult host visual system. This project will provide a greater understanding of the possible mechanisms active in the adult visual system that limit its regenerative capacity and ascertain ways to increase this outgrowth into adult tissue to foster recovery after injury. With this understanding, we can begin to assess means whereby the adult visual system might be treated to restore functon after injury to the system.